Various forms of mobile irrigation devices have irrigation water supplied thereto through a special rubber hose which is dragged through the field behind the irrigation structure. The irrigation structure device is equipped with a water-driven motor driving a winding member upon which one end of a cable is wound and the other end of the cable extends forwardly of the irrigation structure and is suitably anchored whereby the mobile irrigation device is pulled over the ground. However, some mobile irrigation devices of this type utilize large capacity high pressure irrigation guns which oscillate and are rearwardly directed and at the start of a run of the mobile irrigation device along a field the reactionary forces applied to the mobile sprinkler as a result of the rearward discharge of irrigation water therefrom tends to overcome rolling resistance of the wheels of the irrigation device and the frictional drag of the initial short length of hose being dragged behind the irrigation device with the result that the irrigation device tends to move along the field at a rate faster than that which would be determined by the cable being wound on the winding member or winch. The tendency of the mobile irrigation device to "run ahead" of the cable propelling apparatus thereof causes slack in the cable and the cable may wind incorrectly or unevenly on the winding member or drum causing cable and/or winch damage. Further, the front steerable wheels of a mobile irrigation device of this type are controlled by the cable along which the device is pulled and a slack condition in the cable inevitably causes erratic directional movement of the mobile irrigation device. Further, erratic rate of advance of the mobile irrigation device caused by a "run ahead" condition will cause irrigation water delivered thereby to be unevenly applied to the field being irrigated.
In order to prevent the aforementioned "run ahead" condition various attempts have been made at providing mobile irrigation devices with automatically operable wheel brake means actuatable in response to a slack cable condition. Some of these previously designed devices as well as other irrigation devices including some of the general structural features in the instant invention are disclosed in U.S. Pat. Nos. 3,477,643, 3,489,352, 3,684,178 and 3,771,720.